Lecture 4 Working With Lists and Dictionaries

primes = [2, 3, 5, 7, 11, 13]

primes[0]

2

primes[1]

3

for prime  in primes:
    print(prime*prime)

4
9
25
49
121
169

for i in primes:
    print(i*i)

4
9
25
49
121
169

words = "one two three four five six seven".split()

print(words)

['one', 'two', 'three', 'four', 'five', 'six', 'seven']

for word in words:
    print(word[0])

o
t
t
f
f
s
s

for w in words:
    print(w[-1])

e
o
e
r
e
x
n

classroom = {
    "Nisha":1,
    "Indraraj":2,
    "Kaustubh":3,
    "Renuka":4,
    "Sameer":5,
    "Shyreyas":6
}

print(classroom)

{'Nisha': 1, 'Indraraj': 2, 'Kaustubh': 3, 'Renuka': 4, 'Sameer': 5, 'Shyreyas': 6}

for student in classroom:
    print(student, classroom[student])

Nisha 1
Indraraj 2
Kaustubh 3
Renuka 4
Sameer 5
Shyreyas 6

for char in "this is some string":
    print(char) #print on newline

t
h
i
s
 
i
s
 
s
o
m
e
 
s
t
r
i
n
g

for char in "this is some string":
    print(char, end=",") #print on newline

t,h,i,s, ,i,s, ,s,o,m,e, ,s,t,r,i,n,g,

primesqurs = []
for p in primes:
    primesqurs.append(p*p)

print(primesqurs)

[4, 9, 25, 49, 121, 169]

for item in classroom:
    print(item)

Nisha
Indraraj
Kaustubh
Renuka
Sameer
Shyreyas

Questions

• Write a for loop which will print upppercase keys from dictionary
• Write a for loop which will square values from the dictionary and create a new dictionary

emptydict = {}

data = {"a":23,"b":2,"c":45}

for item in classroom:
    print(item.upper())

NISHA
INDRARAJ
KAUSTUBH
RENUKA
SAMEER
SHYREYAS

for item in data:
    print(data[item]**2)

529
4
2025

sqr_data = {}
for item in data:
    sqr_data[item] = data[item]**2

print(sqr_data)

{'a': 529, 'b': 4, 'c': 2025}

Question

• Write a function product which will compute product of all items from a list.

  >>> product([3,4,1])
  12

• Write a function factorial which will find factorial of a number!

  >>> factorial(5)
  120

• Write a function findlens which will find length of every word from given list of words.

  >>> findlens(["one","two","three"])
  {"one":3,
  "two":3,
  "three":5}

def square(x):
    return x*x

def sum_of_squares(x, y):
    return square(x) + square(y)

def product(numbers):
    p = 1
    for n in numbers:
        p = p*n
    return p

product([4, 5, 6, 7])

840

product([1, 2, 3, 4])

24

def factorial(n):
    return product(range(1, n+1))

factorial(5)

120

factorial(20)

2432902008176640000

def findlens(words):
    lens = {}
    for word in words:
        lens[word] = len(word)
    return lens
        

findlens("hello this is some sentence for testing my function".split())

{'hello': 5,
 'this': 4,
 'is': 2,
 'some': 4,
 'sentence': 8,
 'for': 3,
 'testing': 7,
 'my': 2,
 'function': 8}

words = "hello this is some sentence for testing my function".split()
findlens(words)

{'hello': 5,
 'this': 4,
 'is': 2,
 'some': 4,
 'sentence': 8,
 'for': 3,
 'testing': 7,
 'my': 2,
 'function': 8}

Conditions

True

True

False

False

"string"

'string'

x = 4

x == 1

False

x == 4

True

x != 4

False

x != 0

True

x < 4

False

x >= 5

False

words

['hello', 'this', 'is', 'some', 'sentence', 'for', 'testing', 'my', 'function']

"sentence" in words # you can directly check existence of item inside a list

True

"logic" in words

False

"Niket" in classroom # check is the item in left side exists in keys of the dictionary

False

"Nisha" in classroom

True

text = "Let me write some essay here using python"

"some" in text

True

text.isupper()

False

a non empty string, non empty list and a non empty dictionary results as True in if condition while empty string, list, dictionary results in False in if condition

if "logic" in text:
    pass # empty statement
else:
    print("hey ya.. you are here!")

hey ya.. you are here!

numbers = list(range(1, 21))

def filterodd(nums):
    odds = []
    for n in nums:
        if n % 2 == 1:
            odds.append(n)
    return odds

filterodd(numbers)

[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

def filterodd_(nums):
    odds = []
    for n in nums:
        if n%2 == 1:
            odds.append(n)
        return odds #check indentation! this has to be at for level

filterodd_(numbers)

[1]

Question

• Write a function find_words_of_len to find all words of given length from given list.

  >>> words = ["one", "two", "three"]
  >>> find_words_of_len(words, 3)
  ["one",'two"]

• Write a function unique which will remove duplicate entries from the list.

  >>> unique([1, 1, 2, 2, 1, 2, 3, 4, 5, 6, 6, 8])
  [1, 2, 3, 4, 5, 6, 8]

list(set([1, 1, 2, 3, 3, 3, 4, 5, 6]))

[1, 2, 3, 4, 5, 6]

Take home Question

• List of urls is given. Some urls are from same domain, some are from different. Find unique domain names used in the urls.

  urls = ['www.abrakadabra.com/dccEcB/EGdd',
  'www.abrakadabra.com/gADFeD/bcAF',
  'www.abra.com/AGadbb/eagE',
  'www.dabra.com/cffdfD/FCAD',
  'www.abra.com/GFGaBE/dcfc',
  'www.abra.com/gaFegG/Bdaf',
  'www.abrakadabra.com/aGabaf/EEfa',
  'www.dabra.com/ceEgFD/bGgc',
  'www.dabra.com/bDEffC/bcEA']

• Write a function min2 which find minimum from given two numbers. Also write a function min3 which can find minimum number from given 3 numbers. Do not make use of bulit in min function.

def unique(items):
    unique_items = []
    for item in items:
        if item not in unique_items:
            unique_items.append(item)
    return unique_items

unique([1,1,1,2,2,3,3,4,5,4,5,4,6])

[1, 2, 3, 4, 5, 6]